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#lang racket/base
;; Rudimentary spam detection
(require racket/contract
racket/port
memoize
net/http-client
xml
xml/path)
(provide (contract-out [check-ip (-> string? any)]))
(define blacklist-host "api.stopforumspam.org")
;; Returns #f if the lookup failed, if the response is malformed, or
;; if the IP doesn't appear. Return #t if the IP does appear.
;;
;; The result is memoized to avoid querying the server too often.
(define/memo (check-ip ip)
(define-values (status headers contents)
(http-sendrecv blacklist-host
(format "/api?ip=~a" ip)))
(cond ;; only accept 200 OK
[(regexp-match #"200 OK" status)
(define response
(string->xexpr (port->string contents)))
(and response
(equal? "yes" (se-path* '(response appears) response)))]
[else #f]))